In recent years, demands for larger capacity and speeding up of wireless communication have very grown and a method of further improving the effective use efficiency of limited frequency resources has been studied actively. As one of the methods, attention is focused on a technique of using a space domain. One of technologies using a space domain is an adaptive array antenna (adaptive antenna). In the adaptive array antenna, an amplitude and a phase can be adjusted using a weighting coefficient by which a reception signal is multiplied (hereinafter, the weighting coefficient will be referred to as “weight”). As they are adjusted, the adaptive array antenna can strongly receive a signal coming from any desired direction and can suppress an interference wave direction, whereby it is made possible to improve the communication capacity of a system.
Other technologies using a space domain are 1) space division multiple access (hereinafter, SDMA) technology for transmitting to different terminals and 2) spatial multiplex technology for transmitting to the same terminal, different data series using physical channels of the same time, the same frequency, and the same code by using spatial orthogonality in a propagation path.
Information on the SDMA technology is disclosed in non-patent document 1, etc.; if a spatial correlation coefficient between terminals is lower than a predetermined value, SDMA is possible and the throughput and the simultaneous accommodation number of users of a wireless communication system can be improved.
On the other hand, information on the spatial multiplex technology is disclosed in non-patent document 2, for example; spatial multiplex transmission can be realized in a propagation environment in which a transmitter and a receiver have each a plurality of antenna elements and the reception signal correlation between the antennas is low.
In this case, the transmitter transmits a different data series using a physical channel of the same time, the same frequency, and the same code for each antenna element from the provided antennas. The receiver performs separate reception based on the different data series from reception signals at the provided antennas. Accordingly, using a plurality of spatial multiplex streams, it is possible to accomplish speeding up without using multilevel modulation.
To perform SDM transmission, if a transmitter includes antennas of the same number as a receiver, the communication capacity can be enlarged in proportion to the number of antennas in an environment in which a large number of scatters exist between the transmitter and the receiver under a sufficient S/N (signal-to-noise ratio) condition.
Information on an SDM reception method is disclosed in non-patent document 3, for example; transmission series from a plurality of wireless communication apparatus can be separately received using techniques of MMSE (Minimum Mean squared error), ML (Maximum Likelihood), iterative decoding reception, etc.
As the configuration of iterative decoding reception, a parallel interference canceller PIC (parallel Interference Cancellation) for removing interference signals in batch and performing decoding processing and a successive interference canceller SIC (Successive Interference Cancellation) for separating and receiving a spatial multiplex signal successively from a reception signal and performing decoding processing and gradually removing an interference signal from the reception signal are known.
To adopt the iterative decoding reception configuration as a reception method in spatial multiplex transmission, a hard canceller using hard determination as the tentative determination result and a soft canceller using soft determination output are known.
Because of use of a hard determination value, the hard canceller makes it possible to lessen the circuit scale of a receiver and is advantageous in power consumption and cost as compared with the soft canceller.    Non-patent document 1: T. Ohgane et al, “A study on a channel allocation scheme with an adaptive array in SDMA,” IEEE 47th VTC, Page. 725-729, vol. 2 (1997)    Non-patent document 2: G. J. Foschini, “Layered space-time architecture for wireless communication in a fading environment when using multi-element antenna,” Bell Labs Tech. J., pp. 41-59, Autumn 1996    Non-patent document 3: G. J. Foschini, “Layered space-time architecture for wireless communication in a fading environment when using multi-element antenna,” Bell Labs Tech. J., pp. 41-59, Autumn 1996